This invention relates to a face seal system. More specifically, this invention relates to an improved face seal system particularly designed for cooperation with a thrust bearing system in a turbocharger for sealing passage of a turbocharger shaft through a wall.
In a turbocharger, a turbine wheel and a compressor impeller are carried on a common shaft. The turbine wheel is received within a turbine housing for communication with exhaust gases from an engine, whereby the shaft is rotatably driven during engine operation. The shaft is supported by suitable journal bearings and thrust bearings within a center housing connected between the turbine housing and a compressor housing receiving the compressor impeller. The exhaust gas driven turbine wheel thereby drives the compressor impeller to compress charge air for supply to the intake of the engine, all in a well-known manner.
Typically, the rotating shaft in a turbocharger is capable of being driven at relatively high rotational speeds, such as on the order of about 100,000 RPM or more. Such rotational speeds require the use of precision bearing components together with an effective system of bearing lubrication. In this regard, lubricating oil is commonly pumped under pressure to the turbocharger center housing for lubricating the shaft bearings to prevent excessive bearing heating and wear.
The effective lubrication of turbocharger shaft bearings without leakage of oil from the center housing, particularly into the compressor housing, has long been a troublesome problem in the design of turbochargers. Specifically, during normal operation of the turbocharger, localized fluid pressure in the region between the back side of the compressor impeller and the backplate wall separating the center housing from the compressor housing is frequently less than the fluid pressure within the center housing. Thus, a substantial pressure differential is created tending to cause oil leakage from the center housing around the rotating shaft and into the compressor housing. This leakage tendency is substantially enhanced by the high rotational speed of the shaft causing relatively rapid wear of sealing components such as seal rings and the like.
A wide variety of seal systems have been proposed for sealing passage of the turbocharger shaft through the backplate separating the center and compressor housings of the turbocharger. Some of these systems include various seal ring arrangements intended to block oil leakage through the shaft passage. See, for example, U.S. Pat. Nos. 3,397,947; 3,077,296; 2,953,416; 2,785,022; 2,362,667; and 2,054,219. However, these systems are not totally satisfactory in that the seal rings tend to exhibit relatively high rates of wear resulting in premature leakage. Oher arrangements have included slingers and the like in an attempt to move oil away from the region of the leakage path. See, for example, U.S. Pat. Nos. 3,494,679 and 4,157,834. However, these systems also are not altogether successful in eliminating leakage in commercial turbochargers. Still other systems have been proposed including the incorporation of cartridge-type pressure-responsive seal assemblies into the shaft passage between the compressor housing and center housing. See, for example, U.S. Pat. No. 2,393,944. However, these systems introduce into the turbocharger an additional and undesirable leakage path around the outer diameter of the seal cartridge.
The face seal system of this invention overcomes the problems and disadvantages of the prior art by providing an improved face seal system quickly and easily mounted directly into the wall separating the turbocharger compressor and center housing, and including means for varying sealing forces in response to the pressure differential across said wall to limit seal wear.